Conventionally, there has been disclosed an illumination device including a doppler sensor (see, e.g., Japanese Patent Application Publication No. 2009-168778). The illumination device detects a human body by using the doppler sensor and controls a light source to be turned on and off in accordance with the detected result of the human body. In such a kind of illumination device, it is possible to restrict wasteful power consumption that can be caused by user's negligence to turn off the light source in a case where the light source is manually turned on and off.
The doppler sensor is designed to transmit an electric wave (transmission wave), e.g., a millimeter wave, in a detectable range and receive the electric wave (reflection wave) reflected in the detectable range; combine (multiply) an electric signal obtained by receiving the reflection wave and an electric signal having the same frequency as that of the transmission wave; and extract from the obtained electric signal a component of a frequency band corresponding to a moving speed of a human body to thereby acquire a doppler signal. Then, by comparing an amplitude of the doppler signal with a preset comparison threshold, the doppler sensor determines whether or not the human body exists in the detectable range.
A heat ray sensor (so-called passive infrared (PIR) sensor) for detecting a heat ray irradiated from a human body may be used as a sensor for detecting a human body. Compared with the heat ray sensor, the doppler sensor is advantageous in that the doppler sensor is not easily affected by temperature variation of its environment and is capable of detecting a human body that is relatively remote therefrom. Accordingly, the doppler sensor is more adequate for the case of being used in a place whose temperature is variably changed or attached on a high ceiling of a building as compared with the heat ray sensor.
As described in FIGS. 3 and 4, an illumination device 1 as an example of the above-mentioned illumination device includes a straight tube fluorescent lamp 2 having a cylindrical light emitting unit as a light source; a device body 3, fixed to an installation surface (not shown), such as a wall surface, to support the fluorescent lamp 2; and a cover 4 provided to cover the device body 3, the fluorescent lamp 2 being disposed between the cover 4 and the device body 3.
Specifically, the fluorescent lamp 2 is a hot cathode discharge lamp, which is turned on with AC power. The fluorescent lamp 2 is well known in the art, and the detailed description thereof will be omitted.
Hereinafter, the illumination device 1 will be described with reference to FIGS. 3 and 4.
The device body 3 is of a long thin straight tube type and serves to hold a lighting device (not shown) for turning on the fluorescent lamp 2 and two sockets (not shown) that are electrically connected to the lighting device. As for the lighting device, an electronic ballast or a copper/iron ballast, which is well known, may be employed. The lighting device determines whether or not there exists a human body in a detectable range based on an output of a doppler sensor 5. Further, the lighting device turns on the fluorescent lamp 2 if it is determined that there exists a human body in the detectable range while the fluorescent lamp 2 is turned off, and turns off the fluorescent lamp 2 if a continuous time period, during which it is determined that there is not a human body in the detectable range, reaches a preset control time period while the fluorescent lamp 2 is turned on.
The two sockets are respectively provided at opposite end portions of the device body 3 in its longitudinal direction to correspond to caps (not shown) provided at opposite ends of a light emitting unit of the fluorescent lamp 2 in its axial direction, and are detachably coupled to the respective caps. In other words, in a state in which the sockets are respectively coupled to the caps, the fluorescent lamp 2 becomes electrically connected to the lighting device via the sockets, and the longitudinal direction of the device body 3 coincides with the axial direction of the light emitting unit of the fluorescent lamp 2. The lighting device and the sockets are well known and can be easily realized. Thus, the detailed illumination and description thereof are omitted.
The cover 4 is made of a light transmitting material, e.g., glass, and covers the fluorescent lamp 2 when viewed from the side illustrated by the fluorescent lamp 2 (upper side in FIG. 4). For example, the cover 4 serves to protect the fluorescent lamp 2 and to diffuse the light of the fluorescent lamp 2 in order to improve its visual quality.
The cover 4 is of a long thin rectangular flat plate shape, for example. The cover 4 is connected to the device body 3 through adequate iron brackets with a space therebetween such that the longitudinal direction of the cover 4 coincides with the longitudinal direction of the device body 3. In other words, the cover 4 is disposed in such a way that a surface thereof facing the fluorescent lamp 2 is positioned in a parallel relationship with a central axis of the light emitting unit of the fluorescent lamp 2.
In addition, the doppler sensor 5 is fixed to the device body 3 and disposed between the device body 3 and the cover 4. As shown in FIG. 4, a transreceiving unit 51 is provided on an upper portion of the doppler sensor 5 to face the cover 4, the transreceiving unit 51 serving as not only a transmitting unit for transmitting an electric wave from the doppler sensor 5 but also a receiving unit for receiving an electric wave. The detectable range of the doppler sensor 5 is of, e.g., a truncated circular cone shape having the transreceiving unit 51 as its peak and extending through the cover 4. The doppler sensor 5 is also well known and can be easily realized. Thus, the detailed illumination and description thereof are omitted.
However, when the detectable range of the doppler sensor 5 extends through the cover 4, a radiation noise generated from the fluorescent lamp 2 may be reflected by the cover 4 and enter the transreceiving unit 51 as indicated with an arrow A1 in FIG. 4, resulting in a mistake in determination.